Opioid modulation of socially transmitted and spontaneous food preferencesin female mice

The present experiments were conducted to investigate the possible role of endogenous opioid peptides in the social transmission of food preferences i n female mice. In the first experiment, observer animals were injected with 0.5 mg kg(-1) naltrexone, a long-lasting opioid receptor antagonist, 30 mi n prior to a 15-min period of social interaction with a familiar conspecifi c (demonstrator) fed either with a cocoa-flavoured or a plain diet. Afterwa rds, observers underwent a 30-min two-choice test between the cocoa and a m ore palatable, unfamiliar cinnamon diet. The results showed that opioid rec eptor blockade decreased the amount of cocoa diet consumed by the animals w hose demonstrators ate cocoa diet. Experiment 2 showed that naltrexone, adm inistered after the social interaction, strongly attenuated the expression of both a socially acquired preference for the cocoa diet and the spontaneo us preference for the cinnamon diet. A third experiment was then conducted using the shorter-lasting opioid antagonist naloxone. Naloxone (0.5 mg kg(- 1)) administered prior to the social interaction did not impair the acquisi tion of the food preference. Hence, results indicate that a blockade of opi oid activity is sufficient to impair the expression of a socially acquired food preference but not its acquisition. (C) 1999 Elsevier Science B.V. All rights reserved.